Ultraviolet light-emitting device

ABSTRACT

An ultraviolet light-emitting device including a substrate, a first conductive type semiconductor layer disposed on the substrate, a mesa disposed on the first conductive type semiconductor layer and including a second conductive type semiconductor layer and an active layer disposed between the semiconductor layers, a first contact electrode contacting the exposed first conductive type semiconductor layer around the mesa, a second contact electrode contacting the second conductive type semiconductor layer on the mesa, a passivation layer covering the first contact electrode, the mesa, and the second contact electrode and having openings disposed above the first and second contact electrodes, and first and second bump electrodes electrically connected to the first and second contact electrodes through the openings of the passivation layer, in which the mesa has depressions in plan view, and the first and second bump electrodes cover the openings and a portion of the passivation layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is the National Stage Entry of InternationalApplication No. PCT/KR2017/000356, filed Jan. 11, 2017, and claimspriority from Korean Patent Application No. 10-2016-0004351, filed onJan. 13, 2016, and Korean Patent Application No. 10-2016-0171829, filedon Dec. 15, 2016, each of which are incorporated herein by reference forall purposes as if fully set forth herein.

BACKGROUND Field

Exemplary Embodiments of the present invention relate to an ultraviolet(UV) light emitting device, and more particularly, to a UV lightemitting device with improved light extraction efficiency.

Discussion of the Background

In recent years, there has been an increasing interest in a flip-chiptype light emitting device in order to improve luminous efficiency whilesolving problems relating to heat dissipation.

A flip-chip type light emitting device is generally known as havingbetter heat dissipation efficiency than typical light emitting devicesand provides substantially no light shielding so as to have luminousefficacy that is 50% or higher than that of typical light emittingdevices. However, despite such advantages, the flip-chip type lightemitting device some disadvantages.

For example, an n-type semiconductor layer used for UV light emittingdevices has much lower electrical conductivity than metals. Thus, whenelectric current flows through the n-type semiconductor layer, an activelayer, and a p-type semiconductor layer, current crowding may occuralong a path having low electrical resistance. For instance, electricalcurrent flow can be formed between the active layer and the p-typesemiconductor layer along a path having low electrical resistance in then-type semiconductor layer.

Such current crowding causes insufficient light emission over the entireregion of the active layer, thereby deteriorating luminous efficiencyand reliability. In order to overcome this problem, it is necessary toincrease forward voltage and to develop additional technology forincreasing luminous intensity.

SUMMARY

Exemplary embodiments of the present invention provide a light emittingdevice, particularly, a UV light emitting device, which can preventcurrent crowding inside semiconductor layers while improving the degreeof current spreading therein.

The present invention is not limited thereto and other features andadvantages of the present invention will become apparent from thefollowing detailed description.

In accordance with an embodiment of the present invention, a UV lightemitting device includes: a substrate; a first conductivity-typesemiconductor layer disposed on the substrate; a mesa disposed on thefirst conductivity-type semiconductor layer and including a secondconductivity-type semiconductor layer and an active layer interposedbetween the first conductivity-type semiconductor layer and the secondconductivity-type semiconductor layer; a first contact electrodecontacting the first conductivity-type semiconductor layer exposedaround the mesa; a second contact electrode disposed on the mesa andcontacting the second conductivity-type semiconductor layer; apassivation layer covering the first contact electrode, the mesa and thesecond contact electrode, and including openings disposed on the firstcontact electrode and the second contact electrode; and a first bumpelectrode and a second bump electrode electrically connected to thefirst contact electrode and the second contact electrode through theopenings of the passivation layer, respectively, wherein the mesa has aplurality of indentations in plan view and each of the first bumpelectrode and the second bump electrode covers the openings of thepassivation layer and a portion of the passivation layer.

The first contact electrode may contact the first conductivity-typesemiconductor layer at least in the indentations of the mesa.

The UV light emitting device may further include a first pad electrodedisposed on the first contact electrode; and a second pad electrodedisposed on the second contact electrode, wherein the openings of thepassivation layer expose the first pad electrode and the second padelectrode, and the first bump electrode and the second bump electrodemay be connected to the first pad electrode and the second pad electrodethrough the openings, respectively.

The first pad electrode and the second pad electrode may include thesame metallic material.

The UV light emitting device may further include a step pad layerinterposed between the first contact electrode and the first padelectrode.

The UV light emitting device may further include an anti-step patterndisposed on the first pad electrode and the second pad electrode.

The openings of the passivation layer exposing the first contactelectrode may be separated from the mesa and the openings of thepassivation layer exposing the second contact electrode may be disposedwithin an upper region of the mesa.

The first contact electrode may surround the mesa.

The indentations may have an elongated shape in the same direction.

The substrate may be one of a silicon (Si) substrate, a zinc oxide (ZnO)substrate, a gallium nitride (GaN) substrate, a silicon carbide (SiC)substrate, an aluminum nitride (AlN) substrate, and a sapphiresubstrate.

The mesa may have a mirror symmetry structure.

The mesa may have a main branch and a plurality of sub-branchesextending from the main branch.

A portion of the first bump electrode may be disposed on the mesa tooverlap the mesa and the first bump electrode may be spaced apart fromthe mesa by the passivation layer.

The openings of the passivation layer disposed on the first contactelectrode may be partially placed in the indentations.

The first bump electrode may be symmetrically disposed at opposite sidesof the second bump electrode such that the second bump electrode isinterposed therebetween. Furthermore, the first bump electrodes may beconnected to each other.

The second bump electrode may have an arc-shaped end portion.

The second bump electrode may include a plurality of unit electrodesconnected to each other by a connecting portion.

The UV light emitting device may emit deep UV light having a wavelengthof 360 nm or less.

In accordance with an embodiment of the present invention, a UV lightemitting device includes: a substrate; a first conductivity-typesemiconductor layer disposed on the substrate; a mesa disposed on thefirst conductivity-type semiconductor layer, and including a secondconductivity-type semiconductor layer and an active layer interposedbetween the first conductivity-type semiconductor layer and the secondconductivity-type semiconductor layer; a first contact electrodecontacting the first conductivity-type semiconductor layer exposedaround the mesa; a second contact electrode disposed on the mesa andcontacting the second conductivity-type semiconductor layer; apassivation layer covering the first contact electrode, the mesa and thesecond contact electrode, and including openings disposed on the firstcontact electrode and the second contact electrode; and a first bumpelectrode and a second bump electrode electrically connected to thefirst contact electrode and the second contact electrode through theopenings of the passivation layer, respectively, wherein the mesa has aplurality of indentations in plan view and some of the openings of thepassivation layer are disposed outside the mesa and the indentations.

The passivation layer may further include openings disposed inside theindentations, and the openings disposed inside the indentations may beconnected to each other through the openings disposed outside theindentations.

The passivation layer may further include openings disposed inside theindentations, and the openings disposed inside the indentations may beseparated from each other.

According to exemplary embodiments of the present invention, the UVlight emitting device includes a plurality of second bump electrodesdisposed near a first bump electrode such that a separation distancebetween the first bump electrode and end portions of the second bumpelectrodes gradually increases or decreases, thereby allowing chargeshaving a constant current spreading length to spread over a broaderarea. In addition, the first contact electrode is disposed to surround amesa M, thereby enabling more uniform control of a current path from thefirst contact electrode to the second conductivity-type semiconductorlayer through the first conductivity-type semiconductor layer. With thisstructure, the UV light emitting device has reduced resistance in thefirst conductivity-type semiconductor layer, thereby decreasing forwardvoltage thereof.

Furthermore, the mesa is formed with indentations to reduce a currentpath through the first conductivity-type semiconductor layer, therebypreventing current crowding. Furthermore, in the UV light emittingdevice, the first bump electrode and the second bump electrode areformed to partially cover the passivation layer, thereby increasing thesizes of the first bump electrode and the second bump electrode.

It should be understood that the present invention is not limited to theaforementioned effects and includes all advantageous effects deduciblefrom the detailed description of the present invention or the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a plan view of a light emitting device according to oneexemplary embodiment of the present invention.

FIG. 2 and FIG. 3 are cross-sectional views taken along line A-A′ andline B-B′ of FIG. 1.

FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are cross-sectionalviews illustrating a method of manufacturing the light emitting deviceaccording to an exemplary embodiment of the present invention, all ofwhich are taken along line B-B′ of FIG. 1.

FIG. 10, FIG. 11, and FIG. 12 are plan views of UV light emittingdevices according to exemplary embodiments of the present invention.

FIG. 13 is a perspective view of a light emitting device packageaccording to one exemplary embodiment of the present invention.

FIG. 14 is a plan view of a light emitting device according to anotherexemplary embodiment of the present invention.

FIG. 15A and FIG. 15B are cross-sectional views taken along lines C-C′and D-D′ of FIG. 14.

FIG. 16A, FIG. 16B, FIG. 17A, FIG. 17B, FIG. 18A, FIG. 18B, FIG. 19A,and FIG. 19B are plan views and cross-sectional views illustrating amethod of manufacturing the light emitting device of FIG. 14.

FIG. 20, FIG. 21, FIG. 22, and FIG. 23 are plan views of UV lightemitting devices according to exemplary embodiments of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, the present invention is not limited to the embodimentsdisclosed herein and can also be implemented in different forms. Inaddition, portions irrelevant to the present invention will be omittedfor clarity in the accompanying drawings and like components will bedenoted by the same or like reference numerals throughout thespecification.

When an element or layer is referred to as being “connected to” or“coupled to” another element or layer throughout the specification, itcan be directly connected or coupled to the other element or layer, orintervening elements or layers can be present. In addition, the terms“comprises,” “comprising,” “including,” and “having” are inclusive andtherefore specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a plan view of a light emitting device according to oneexemplary embodiment of the present invention, and FIG. 2 and FIG. 3 arecross-sectional views taken along line A-A′ and line B-B′ of FIG. 1.

Referring to FIG. 1, FIG. 2, and FIG. 3, a light emitting device 100according to one exemplary embodiment of the present invention mayinclude a first substrate 110.

The first substrate 110 is provided for growth of a single crystalsemiconductor thereon and may have a first plane 110 a and a secondplane 110 b opposing the first plane 110 a. The first plane 110 a is anupper surface of the first substrate 110 on which the single crystalsemiconductor will be grown, and the second plane 110 b is a lowersurface thereof.

The first substrate 110 may include a zinc oxide (ZnO) substrate, agallium nitride (GaN) substrate, a silicon carbide (SiC) substrate, analuminum nitride (AlN), and a sapphire substrate. For example, the firstsubstrate 110 may be formed of a transparent material includingsapphire, which has a high degree of crystal orientation and allowsprecise polishing to provide no flaw or stain. The first plane 110 a andthe second plane 110 b of the first substrate 110 may have a rectangularshape.

The light emitting device 100 according to the illustrated exemplaryembodiment may include a first bump electrode 151 and a second bumpelectrode 152 formed on the first plane 110 a of the first substrate110. The first bump electrode 151 and the second bump electrode 152 mayhave opposite polarities. For example, the first bump electrode 151 maybe an N-type bump electrode and the second bump electrode 152 may be aP-type bump electrode.

The first bump electrode 151 may have an axial direction of a firstdirection on the first plane 110 a of the first substrate 110, and thesecond bump electrode 152 may have an axial direction of a seconddirection thereon. The first direction may be a direction parallel toone side of the first plane 110 a of the first substrate 110, and thesecond direction may be a direction perpendicular to the firstdirection. For example, the first direction may be an X-axis directionand the second direction may be a Y-axis direction.

The second bump electrode 152 may include a plurality of unit electrodes153 to form a plurality of current paths, thereby improving currentspreading. The unit electrodes 153 may have a constant length and aconstant width and may be arranged parallel to each other. Each of theunit electrodes 153 may be connected to adjacent unit electrodes via aconnecting portion 154 disposed at the center of the first plane.Accordingly, the unit electrodes 153 may be symmetrically arranged withreference to the connecting portion 154 at the center of the firstplane. Since the connecting portion 154 is formed to be orthogonal toeach of the unit electrodes 153, the first bump electrode 151 and theconnecting portion 154 may be disposed to be parallel to each other.

Each of the unit electrodes 153 has an end portion 153 a near the firstbump electrode 151. Particularly, the unit electrodes 153 may be formedsuch that a separation distance between the end portion 153 a of each ofthe unit electrodes 153 and an imaginary axis X parallel to the axialdirection of the first bump electrode 151 gradually increases ordecreases. For example, the end portion 153 a of each of the unitelectrodes 153 has an arc shape protruding toward the first bumpelectrode 151, thereby minimizing current crowding between the firstbump electrode 151 and the second bump electrode 152.

A pair of first bump electrodes 151 may be disposed at opposite sides ofthe second bump electrode 152 to be symmetrical to each other, such thatelectric current can be injected through the pair of first bumpelectrodes 151, thereby further improving current spreading efficiency.That is, the first bump electrode 151 may be further formed to beparallel to the other side of the first plane 110 a of the firstsubstrate 110. The second bump electrode 152 may be interposed betweenthe pair of first bump electrodes 151 and both end portions 153 a of thesecond bump electrode 152 may be disposed near the first bump electrodes151, respectively.

Referring to FIG. 2 and FIG. 3, the light emitting device 100 may be aUV light emitting device capable of emitting light in the UV wavelengthrange. For example, a UV light emitting device according to oneexemplary embodiment may emit deep UV light having a wavelength of 360nm or less.

The light emitting device 100 may include the first substrate 110 and alight emitting diode 120 disposed on the first substrate 110, and havinga semiconductor stack structure.

A buffer layer (not shown) may be further formed on the first plane 110a of the first substrate 110 to relieve lattice mismatch between thefirst substrate 110 and a first conductivity-type semiconductor layer121. The buffer layer may be composed of a single layer or multiplelayers. The buffer layer composed of multiple layers may include a lowtemperature buffer layer and a high temperature buffer layer.

The light emitting diode 120 (e.g., semiconductor stack) is a lightemitting structure for converting energy into light throughrecombination of electrons and holes, and may be formed on the firstsubstrate 110, which is subjected to surface treatment through a wet ordry process using a semiconductor thin film growth apparatus.

The light emitting diode 120 may include the first conductivity-typesemiconductor layer 121, an active layer 122, and a secondconductivity-type semiconductor layer 123, which are sequentiallystacked on the first plane 110 a of the first substrate 110.

The first conductivity-type semiconductor layer 121 may be disposed onthe first plane 110 a of the first substrate 110 and may be partiallyexposed, as shown in FIG. 2. Specifically, the partially exposed regionof the first conductivity-type semiconductor layer 121 may be formed bymesa etching part of the active layer 122 and the secondconductivity-type semiconductor layer 123. During mesa etching, thefirst conductivity-type semiconductor layer 121 may also be partiallyremoved by etching. As a result, a mesa including the active layer 122and the second conductivity-type semiconductor layer 123 is formed onthe first conductivity-type semiconductor layer 121. As shown in FIG. 2and FIG. 3, the second bump electrode 152 is disposed on the mesa andthe first bump electrode 151 is separated from the mesa. The mesa has ashape similar to that of the second bump electrode 152 and hasindentations each being disposed between the unit electrodes 153. Forexample, the mesa may include a main branch disposed under theconnecting portion 154 and sub-branches corresponding to portions of theunit electrodes 153 extending from opposite sides of the connectingportion 154.

The first conductivity-type semiconductor layer 121 may be formed of anIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1) based Group III-Vcompound semiconductor doped with first conductivity-type dopants, forexample, N-type dopants, and may be composed of a single layer ormultiple layers. Examples of the N-type dopants may include Si, Ge, Sn,and the like. In particular, the first conductivity-type semiconductorlayer 121 has a relatively high bandgap to allow UV light generated fromthe active layer 122 to pass therethrough.

The active layer 122 may be disposed on the first conductivity-typesemiconductor layer 121 and generates light through recombination ofelectrons and holes supplied from the first conductivity-typesemiconductor layer 121 and the second conductivity-type semiconductorlayer 123. According to one exemplary embodiment, the active layer 122may have a multi-quantum well structure in order to improve efficiencyin recombination of electrons and holes. Compositional elements andratio of the active layer 122 may be determined to emit light having adesired wavelength, for example, UV light having a peak wavelength inthe range of 200 nm to 360 nm.

The second conductivity-type semiconductor layer 123 may be disposed onthe active layer 122 and may be formed of an In_(x)Al_(y)Ga_(1-x-y)N(0≤x≤1, 0≤y≤1, 0≤x+y≤1) based compound semiconductor doped with secondconductivity-type dopants, for example, P-type dopants. The secondconductivity-type semiconductor layer 123 may be composed of a singlelayer or multiple layers.

A first pad electrode 131 and a second pad electrode 132 may be formedon the first conductivity-type semiconductor layer 121 and the secondconductivity-type semiconductor layer 123, respectively. The first padelectrode 131 and the second pad electrode 132 may include Ni, Cr, Ti,Al, Ag, or Au. The first pad electrode 131 may be electrically connectedto the exposed portion of the first conductivity-type semiconductorlayer 121, and the second pad electrode 132 may be electricallyconnected to the exposed portion of the second conductivity-typesemiconductor layer 123.

The light emitting device 100 may further include a step pad layer 133between the first conductivity-type semiconductor layer 121 and thefirst pad electrode 131. The step pad layer 133 compensates for a stepdifference, such that the elevation of the first pad electrode 131corresponds to the elevation of the second pad electrode 132. That is,due to mesa etching of the first conductivity-type semiconductor layer121, the first pad electrode 131 may be placed at a lower location thanthe second pad electrode 132 without the step pad layer 133. However,the elevation of the first pad electrode 131 may become offset by thestep pad layer 133 under the first pad electrode 131. The step pad layer133 may include, for example, Ti and Au.

In addition, the light emitting device 100 may further include the firstcontact electrode 141 and a second contact electrode 142 between thefirst conductivity-type semiconductor layer 121 and the step pad layer133, and between the second conductivity-type semiconductor layer 123and the second pad electrode 132 in order to improve ohmic contactcharacteristics. The first contact electrode 141 may include, forexample, Cr, Ti, Al and Au, and the second contact electrode 142 mayinclude, for example, Ni and Au.

Here, the first contact electrode 141 is an electrode for forming ohmiccontact characteristics with the first conductivity-type semiconductorlayer 121, and is disposed in the exposed region of the firstconductivity-type semiconductor layer 121 excluding a mesa region inorder to improve current spreading of the UV light emitting device. Thefirst contact electrode 141 surrounds the mesa and may also be placedinside the indentations of the mesa. The first contact electrode 141 mayinclude a reflective material.

The reflective material serves to reflect UV light, which has beenreflected from the first substrate 110 toward the first contactelectrode 141, back toward the first substrate 110, thereby improvinglight extraction efficiency.

The reflective material may be formed of a metallic material having goodconductivity. The reflective material may include, for example, Ag, Ni,Al, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and Hf. In particular, thereflective material may include aluminum (Al) having high reflectance inthe UV wavelength band, and may be deposited not only in a planarstructure, but also in a matrix of islands, in a plurality of lines, orin a mesh structure.

In one exemplary embodiment, the light emitting device 100 may furtherinclude a passivation layer 160 that serves to protect the lightemitting diode 120 from external environments.

The passivation layer 160 may be formed of silicon oxide or aninsulation material including silicon oxide. As shown in FIG. 2 and FIG.3, the passivation layer 160 covers the first pad electrode 131, thesecond pad electrode 132, and the mesa. Here, the passivation layer 160may be provided in the form of partially exposed regions on the surfacesof the first pad electrode 131 and the second pad electrode 132, suchthat the first bump electrode 151 is electrically connected to thesecond bump electrode 152 therethrough. That is, the passivation layer160 has openings that expose the surfaces of the first pad electrode 131and the second pad electrode 132. The passivation layer 160 may beformed of an insulator including an oxide or a nitride, particularly,silicon oxide.

The light emitting device 100 may be mounted on the second substrate 200(see FIG. 8 and FIG. 9) in a flip-chip form. In this case, the lightemitting device 100 may include the first bump electrode 151 and thesecond bump electrode 152 so as to be electrically connected to thesecond substrate 200.

The first bump electrode 151 may be disposed on the first pad electrode131 and the second bump electrode 152 may be disposed on the second padelectrode 132. The first bump electrode 151 and the second bumpelectrode 152 may include, for example, Ti, Au, and Cr.

The second substrate 200 includes a first electrode portion 210 and asecond electrode portion 220 on one surface thereof such that the firstand second bump electrodes 151, 152 of the light emitting device 100 canbe electrically and physically connected to the first and secondelectrode portions 210, 220, respectively.

Here, the bump electrodes 151, 152 may be formed to cover the surfacesof the pad electrodes 131, 132 and some regions of the surface of thepassivation layer 160. That is, the bump electrodes 151, 152 cover theopenings of the passivation layer 160 and may be partially disposed onthe passivation layer 160 to overlap the passivation layer 160. Forbonding reliability, a portion of the passivation layer 160 isinterposed between the pad electrodes 131, 132 and the bump electrodes151, 152, and the bump electrodes 151, 152 are formed to cover theexposed portions of the pad electrodes 131, 132 and some regions on thesurface of the passivation layer 160.

On the other hand, anti-step patterns 161, 162 may be interposed betweenthe pad electrodes 131, 132 and the bump electrodes 151, 152. Forexample, the anti-step patterns 161, 162 may be placed in the openingsof the passivation layer 160.

FIG. 4 to FIG. 9 are cross-sectional views illustrating a method ofmanufacturing the light emitting device according to an exemplaryembodiment of the present invention. Here, FIG. 4 to FIG. 9 are takenalong line B-B′ of FIG. 1.

Referring to FIG. 4, a first conductivity-type semiconductor layer 121,an active layer 122, and a second conductivity-type semiconductor layer123 are formed on a first substrate 110.

Here, the first conductivity-type semiconductor layer 121, the activelayer 122, and the second conductivity-type semiconductor layer 123 maybe formed by forming respective semiconductor layers using asemiconductor layer formation method well-known in the art, for example,metal organic chemical vapor deposition (MOCVD), molecular beamdeposition, epitaxial deposition, or others, followed by partiallyetching the second conductivity-type semiconductor layer 123 and theactive layer 122 to expose some regions of the surface of the firstconductivity-type semiconductor layer 121. As a result, a mesa includingthe active layer 122 and the second conductivity-type semiconductorlayer 123 is formed.

Referring to FIG. 5, a first pad electrode 131 is formed on the firstconductivity-type semiconductor layer 121, and a second pad electrode132 is formed on the second conductivity-type semiconductor layer 123.

The pad electrodes 131, 132 may be formed of Ti/Au. Contact electrodes141, 142 may be formed before formation of the pad electrodes 131, 132.The contact electrode 141 is formed on the first conductivity-typesemiconductor layer 121 and the contact electrode 142 is formed on thesecond conductivity-type semiconductor layer 123. For example, thecontact electrode 141 may be formed of Ti/Al layers and the contactelectrode 142 may be formed of Ni/Au layers.

Furthermore, a step pad layer 133 may be formed on the contact electrode141. The step pad layer 133 compensates for a step difference due to themesa to allow an upper surface of the first pad electrode 131 to besubstantially flush with an upper surface of the second pad electrode132.

Referring to FIG. 6, an insulation layer is formed on the surface of thefirst substrate 110, on which the first conductivity-type semiconductorlayer 121, the active layer 122, and the second conductivity-typesemiconductor layer 123 are formed, and is partially removed by etchingto open some regions on the surfaces of the pad electrodes 131, 132 toform the passivation layer 160.

That is, the passivation layer 160 is formed by forming the insulationlayer over the entire surface of the first substrate 110, followed byexposing some regions of the pad electrodes 131, 132. As a result, thepassivation layer 160 serves to protect the first and secondconductivity-type semiconductor layers 121, 123 and the active layer 122by covering the side surfaces of the second conductivity-typesemiconductor layer 123 and the active layer 122 exposed by etching, andthe surfaces of the first conductivity-type semiconductor layer 121 andthe second conductivity-type semiconductor layer 123 exposed afterformation of the pad electrodes 131, 132.

By this process, it is possible to form the light emitting device 100including the semiconductor layers 121,122,123, the pad electrodes 131,132 and the passivation layer 160 on the first substrate 110.

Referring to FIG. 7, a first bump electrode 151 and a second bumpelectrode 152 are formed on the first and second pad electrodes 131, 132of the light emitting device 100, respectively.

The bump electrodes 151, 152 may be formed to cover the surfaces of thepad electrodes 131, 132 and some regions of the surface of thepassivation layer 160. That is, for bonding reliability, a portion 150 aof the passivation layer 160 is interposed between the pad electrodes131, 132 and the bump electrodes 151, 152, and the bump electrodes 151,152 are formed to cover the exposed portions of the pad electrodes 131,132 and some regions of the surface of the passivation layer 160.Accordingly, protrusions 151 a, 152 a may protrude upwards from upperouter peripheries of the bump electrodes 151, 152, which cover someregions of the surface of the passivation layer 160. Due to formation ofthe protrusions 151 a, 152 a, the bump electrodes 151, 152 are generallyformed to have stepped upper surfaces, thereby making it difficult toachieve stable bonding between the bump electrodes 151, 152 and theelectrode portions 210, 220 upon mounting of the light emitting device100 on the second substrate 200.

Accordingly, a first anti-step pattern 161 and a second anti-steppattern 162 may further be formed on the first pad electrode 131 and thesecond pad electrode 132, respectively. Due to formation of the firstand second anti-step patterns 161, 162, anti-step portions 151 b, 152 bare formed in central regions of upper surfaces of the bump electrodes151, 152 corresponding to the height of the protrusions 151 a, 152 aformed at the outer peripheries of the bump electrodes 151, 152, wherebythe overall upper surfaces of the bump electrodes 151, 152 can have aconsiderably flat shape instead of having stepped portions.

The first and second anti-step patterns 161, 162 may be silicon oxide(SiO₂) patterns formed of the same material as the passivation layer160. That is, the first and second anti-step patterns 161, 162 may beformed by etching the passivation layer 160 such that a portion of thepassivation layer 160 remains on the pad during etching for exposure ofthe pad after formation of the passivation layer 160.

Referring to FIG. 8 and FIG. 9, the light emitting device 100 accordingto an exemplary embodiment may be mounted on the second substrate 200 inthe form of a flip-chip bonded structure by a thermo-compression (T/C)method. The second substrate 200 may be a submount on which the lightemitting diode 120 will be mounted.

The second substrate 200 may include a first electrode portion 210 and asecond electrode portion 220 on one surface thereof, such that the firstbump electrode 151 and the second bump electrode 152 of the lightemitting device 100 can be connected to the first electrode portion 210and the second electrode portion 220, respectively. For example, thefirst electrode may be an N-electrode and the second electrode may be aP-electrode.

Here, in order to compensate for a height difference between the bumpelectrodes 151, 152, the first electrode portion 210 and the secondelectrode portion 220 may have different heights. For example, the firstelectrode portion 210 has a greater thickness than the second electrodeportion 220 to compensate for a step caused by the height differencebetween the bump electrodes 151, 152.

The first and second electrode portions 210, 220 may include gold or agold-containing compound (for example, AuSn) to secure ease of flipbonding to the bump electrodes 151, 152, electrical conductivity, andthermal conductivity.

In order to mount the light emitting device 100 on the second substrate200, the light emitting device 100 and the second substrate 200 arearranged so as to correspond to each other with reference to the bumpelectrodes 151, 152 and the first and second electrode portions 210,220, followed by heating the bump electrodes 151, 152 to a presettemperature.

While a preset pressure is applied to the first substrate 110 or thesecond substrate 200, the temperature of the bump electrodes 151, 152 isgradually increased. After the increased temperature of the bumpelectrodes 151, 152 is maintained for a preset period of time, thepressure is released and the bump electrodes 151, 152 are cooled to roomtemperature such that the bump electrodes 151, 152 can be flip-chipbonded to the first and second electrode portions 210, 220, therebycompleting mounting of the light emitting device 100 including the bumpelectrodes 151, 152 to the second substrate 200 that includes the firstand second electrode portions 210, 220.

Here, protrusions 151 a, 152 a and anti-step portions 151 b, 152 b areformed at the same height on bump electrodes 151, 152 so as to minimizea step thereon, thereby improving bonding reliability with respect tothe first and second electrode portions 210, 220.

FIG. 10 to FIG. 12 are plan views of UV light emitting devices accordingto exemplary embodiments of the present invention.

In a UV light emitting device shown in FIG. 10, a first bump electrode10 is disposed at one corner of a substrate having a substantiallyrectangular shape, such that an axial direction of the first bumpelectrode 10 is placed in a diagonal direction, and a plurality ofsecond bump electrodes 20 is formed to be orthogonal to the axialdirection of the first bump electrode 10. The second bump electrodes 20may be disposed on a mesa having indentations and connected to eachother. When the first bump electrode 10 is disposed at one corner of thesubstrate and the second bump electrodes 20 are disposed to occupy mostof an upper surface of the substrate, the light emitting device has anincreased light emitting area. However, in the light emitting deviceaccording to this exemplary embodiment, the first bump electrode 10 isbiased to one corner of the substrate, thereby causing reduction inluminous intensity due to decrease in current density.

In a UV light emitting device shown in FIG. 11, a pair of first bumpelectrodes 30 is disposed at opposite sides of a substrate having asubstantially rectangular shape and a plurality of second bumpelectrodes 40 is formed between the first bump electrodes 30 to beparallel to the first bump electrodes 30. The second bump electrodes 40may be connected to each other by a connecting portion 41. Here, thefirst bump electrodes 30 and the second bump electrodes 40 are disposedto be parallel to one another, thereby increasing forward voltage due tocurrent crowding.

In a UV light emitting device shown in FIG. 12, a pair of first bumpelectrodes 50 is disposed at opposite sides of a substrate and aplurality of second bump electrodes 60 having an uneven width isdisposed between the first bump electrodes 50 so as to be orthogonal tothe axial direction of the first bump electrode 50. The second bumpelectrodes 60 may be connected to each other by a connecting portion 61.The first bump electrodes 50 and the second bump electrodes 60 areformed such that the axial direction of each of the first bumpelectrodes 50 is perpendicular to the axial direction of each of thesecond bump electrodes 60, and the first bump electrodes 50 have adifferent width than the second bump electrodes 60 adjacent thereto. Inaddition, at least one of the second bump electrodes 60 may extend toone corner of the substrate. Here, current spreading can be deterioratednear the extended portion of the second bump electrode.

FIG. 13 is a perspective view of a light emitting device packageaccording to one exemplary embodiment of the present invention.

Referring to FIG. 13, a light emitting device package 1000 according toan exemplary embodiment may include a package body 1100 and a lightemitting device 100 mounted on the package body 1100.

The package body 1100 has a cavity 1110 depressed on one surface thereofsuch that an inclined surface 1111 can be formed around the lightemitting device 100. The inclined surface 1111 can improve lightextraction efficiency of the light emitting device package.

The package body 1100 is divided into a first electrode portion 1200 anda second electrode portion 1300 by an insulating portion 1400 to beelectrically isolated from each other.

The package body 1100 may include a silicone material, a synthetic resinmaterial, or a metallic material. For example, in order to improve heatdissipation upon discharge of UV light from the light emitting device100, the package body 1100 may be formed of an aluminum material.Accordingly, the first electrode portion 1200 and the second electrodeportion 1300 can improve luminous efficiency by reflecting light emittedfrom the light emitting device 100 and also serve to discharge heatgenerated from the light emitting device 100.

The light emitting device 100 may be electrically connected to the firstelectrode portion 1200 and the second electrode portion 1300 by aconnection member 1600, such as a metal wire, to receive electric powertherethrough.

In a state of being mounted on the second substrate, the light emittingdevice 100 may be mounted on the cavity 1110 of the package body 1100and may be electrically connected to the first electrode portion 1200and the second electrode portion 1300 by a metal wire. Reference numeral1500 indicates a Zener diode, which is a constant voltage diode.

FIG. 14 is a plan view of a light emitting device 300 according toanother exemplary embodiment of the present invention, and FIG. 15A andFIG. 15B are cross-sectional views taken along lines C-C′ and D-D′ ofFIG. 14.

Referring to FIG. 14, FIG. 15A, and FIG. 15B, a light emitting device300 includes a substrate 310, a semiconductor stack (e.g., lightemitting diode) 320, which includes a first conductivity-typesemiconductor layer 321, an active layer 322, and a secondconductivity-type semiconductor layer 323, a first contact electrode341, a second contact electrode 342, a first pad electrode 331, a secondpad electrode 332, a passivation layer 360, a first bump electrode 351,a second bump electrode 352, and an anti-reflection layer 370.

The substrate 310, the first conductivity-type semiconductor layer 321,the active layer 322, and the second conductivity-type semiconductorlayer 323 are similar to those described with reference to FIG. 1, FIG.2, and FIG. 3, and thus detailed descriptions thereof will be omitted toavoid redundancy.

As described above, the semiconductor stack 320 includes the firstconductivity-type semiconductor layer 321 and a mesa M disposed on thefirst conductivity-type semiconductor layer 321, in which the mesa Mincludes the active layer 322 and the second conductivity-typesemiconductor layer 323. The mesa M may also include a portion of thefirst conductivity-type semiconductor layer 321.

On the other hand, the mesa M is disposed in some region on the firstconductivity-type semiconductor layer 321. Generally, the mesa M isformed by sequentially growing the first conductivity-type semiconductorlayer 321, the active layer 322, and the second conductivity-typesemiconductor layer 323, followed by patterning the secondconductivity-type semiconductor layer 323 and the active layer 322through mesa etching.

As described with reference to FIG. 1, the mesa M has indentations. Thatis, the mesa M may have a structure including a main branch andsub-branches, in which the indentations are formed between thesub-branches. Such a structure can be described as a structure whereinunit mesas are connected to each other by a connection mesa. Here, acentral portion extending to the connection mesa corresponds to the mainbranch, and the unit mesas extending from opposite sides of the mainbranch correspond to the sub-branches.

The widths of the sub-branches may be two times less than the width ofthe first conductivity-type semiconductor layer 321 exposed between thesub-branches. With the structure wherein the sub-branches are formed tohave a relatively small width and are disposed over a broad region onthe substrate 310, the side surface of the mesa M has an increasedsurface area. The main branch may have a broader width than thesub-branches, without being limited thereto. Alternatively, the width ofthe main branch may be less than or equal to the width of thesub-branches.

Since the mesa M includes the sub-branches having a relatively narrowwidth, the light emitting device package can reduce current pathsthrough the first conductivity-type semiconductor layer 321 having arelatively large width, thereby reducing current crowding.

Referring again to FIG. 14, FIG. 15A, and FIG. 15B, the first contactelectrode 341 is disposed on the first conductivity-type semiconductorlayer 321 exposed around the mesa M. The first contact electrode 341 maybe formed by depositing a plurality of metal layers, followed byalloying the metal layers through rapid thermal alloying (RTA). Thefirst contact electrode 341 may include a reflective material. Forexample, the first contact electrode 341 may be formed by sequentiallydepositing Cr/Ti/Al/Ti/Au, followed by alloying through the RTA processat a temperature of, for example, 935° C., for several to dozens ofseconds. Accordingly, the first contact electrode 341 becomes an alloylayer containing Cr, Ti, Al, and Au.

The first contact electrode 341 surrounds the mesa M along thecircumference of the mesa M. In addition, the first contact electrode341 is disposed in regions between the sub-branches, that is, in theindentations of the mesa M. The first contact electrode 341 is separatedfrom the mesa M by a predetermined distance and may be formed in most ofthe upper region of the first conductivity-type semiconductor layer 321.The first contact electrode 341 is formed along the side surface of themesa M. This structure provides a region between the mesa M and thefirst contact electrode 341, in which the first contact electrode 341 isabsent. Thus, light emitted through the side surface of the mesa M canreenter the first conductivity-type semiconductor layer 321 through thisregion, and can be emitted outside through the substrate 310. Aseparation distance between the first contact electrode 341 and the mesaM may be constant along the circumference of the mesa M, without beinglimited thereto.

After formation of the first contact electrode 341, the second contactelectrode 342 is formed on the mesa M. The second contact electrode 342may be formed by depositing, for example, Ni/Au, followed by RTA atabout 590° C. for 80 seconds. The second contact electrode 342 formsohmic contact with the second conductivity-type semiconductor layer 323and covers most of the upper region of the mesa M, for example, 80% ormore of the upper region thereof.

The first pad electrode 331 and the second pad electrode 332 are formedon the first contact electrode 341 and the second contact electrode 342,respectively. The first pad electrode 331 and the second pad electrode332 may be formed of the same metal by the same process. For example,the first and second pad electrodes 331, 332 may be composed of a Tilayer (300 Å)/Au layer (7,000 Å)/Ti layer (50 Å).

However, the inventive concepts are not limited thereto. As describedabove, for example, a step pad layer 133 may be interposed between thefirst pad electrode 331 and the first contact electrode 341.

Referring back to FIG. 14, FIG. 15A, and FIG. 15B, the first padelectrode 331 and the second pad electrode 332 are illustrated as havingthe same areas as the first contact electrode 341 and the second contactelectrode 342 and as being disposed thereon, respectively. However, theinventive concepts are not limited thereto. For example, the first padelectrode 331 and the second pad electrode 332 may have smaller areasthan the first contact electrode 341 and the second contact electrode342 to be disposed thereon, respectively, or may have larger areas thanthe first contact electrode 341 and the second contact electrode 342 tocover upper and side surfaces thereof. Since the first and second padelectrodes 331, 332 covers not only the upper surfaces of the contactelectrodes 341, 342 but also the side surfaces thereof, the first andsecond pad electrodes 331, 332 can protect the first and second contactelectrodes 341, 342 from solder during solder or AuSn bonding.

The passivation layer 360 covers the mesa M, the first pad electrode331, and the second pad electrode 332. The passivation layer 360 has anopening 360 a exposing the first pad electrode 331 and an opening 360 bpartially exposing the second pad electrode 332 on the mesa M. Theopening 360 a overlaps the first contact electrode 341 and the opening360 b overlaps the second contact electrode 342.

The openings 360 a may be disposed along an edge of the substrate 310and also disposed inside the indentations of the mesa M, as indicated bya dotted line of FIG. 14. The openings 360 a disposed inside theindentations may communicate with each other through the opening 360 adisposed along the edge of the substrate 310. Alternatively, theopenings may be separated from each other.

The openings 360 b may be disposed on the mesa M to communicate witheach other as a single opening. Alternatively, a plurality of openings360 b may be disposed on the mesa M to be separated from each other.

The first bump electrode 351 covers the openings 360 a and is connectedto the first pad electrode 331 through the openings 360 a. The firstbump electrode 351 is electrically connected to the firstconductivity-type semiconductor layer 321 through the first padelectrode 331 and the first contact electrode 341. The first bumpelectrodes 351 are symmetrically disposed at opposite sides of thesecond bump electrode 352 and are connected to each other, with thesecond bump electrode 352 interposed therebetween.

In the exemplary embodiment described with reference to FIG. 1, thefirst bump electrodes 151 are separated from the mesa M. On thecontrary, in this exemplary embodiment, the first bump electrode 351 ispartially disposed on the mesa M and the second pad electrode 33,2 andis insulated from the mesa M and the second pad electrode 332 by thepassivation layer 360. Since the first bump electrode 351 may be formedto overlap the mesa M, the first bump electrode 351 may be formed in arelatively large area, and thus, directly contact the first padelectrode 331 inside the indentations of the mesa M.

The second bump electrode 352 covers the opening 360 b and is connectedto the second pad electrode 332 through the opening 360 b. The secondbump electrode 352 is electrically connected to the secondconductivity-type semiconductor layer 323 through the second padelectrode 332 and the second contact electrode 342. The second bumpelectrode 352 may have a structure including unit electrodes 353 and aconnecting portion 354, like the exemplary embodiment described withreference to FIG. 1.

Each of the first bump electrode 351 and the second bump electrode 352may be formed of, for example, Ti/Au/Cr/Au.

An anti-reflection layer 370 may be disposed on a lower surface of thesubstrate 310. The anti-reflection layer 370 may be a transparentinsulation layer, such as a SiO₂ layer, and have a thicknesscorresponding to, for example, integer times ¼ of a UV wavelength.Alternatively, the anti-reflection layer 370 may be composed of a bandpass filter formed by repeatedly stacking layers having differentindices of refraction.

In this exemplary embodiment, the first bump electrode 351 partiallyoverlaps the mesa M and partially cover the side surface of the mesa M.Accordingly, the first bump electrode 351 can reflect light emittedthrough the side surface of the mesa M to reenter the mesa M, therebyreducing light loss.

FIG. 16 to FIG. 19 are views illustrating a method of manufacturing thelight emitting device shown in FIG. 14. FIGS. 16A, 17A, 18A, and 19A areplan views and FIGS. 16B, 17B, 18B, and 19B are cross-sectional viewsthereof taken along line C-C′ of the plan view, respectively.

Referring to FIG. 16A and FIG. 16B, a first conductivity-typesemiconductor layer 321, an active layer 322, and a secondconductivity-type semiconductor layer 323 are formed on a substrate 310,followed by etching the second conductivity-type semiconductor layer 323and the active layer 322 to form a mesa M, as described with referenceto FIG. 4.

The mesa M is formed to have a shape including a main branch Mb andsub-branches Sb, and has indentations Cp between the sub-branches Sb. Inthe mesa M with the indentations, the sub-branches Sb can be formed tohave a relatively narrow width.

Referring to FIG. 17A and FIG. 17B, a first contact electrode 341 isformed on the first conductivity-type semiconductor layer 321 and asecond contact electrode 342 is formed on the second conductivity-typesemiconductor layer 323.

The first contact electrode 341 is disposed on the firstconductivity-type semiconductor layer 321 exposed around the mesa M. Thefirst contact electrode 341 may be formed by depositing a plurality ofmetal layers, followed by alloying the metal layers through rapidthermal alloying (RTA). In addition, the first contact electrode 341 mayinclude a reflective material. For example, the first contact electrode341 may be formed by sequentially depositing Cr/Ti/Al/Ti/Au, followed byalloying through the RTA process at a temperature of, for example, 935°C., for several to dozens of seconds. Accordingly, the first contactelectrode 341 becomes an alloy layer containing Cr, Ti, Al, and Au.

After formation of the first contact electrode 341, the second contactelectrode 342 is formed on the mesa M. The second contact electrode 342may be formed by depositing, for example, Ni/Au, followed by RTA atabout 590° C. for 80 seconds. The second contact electrode 342 formsohmic contact with the second conductivity-type semiconductor layer 323and covers most of the upper region of the mesa M, for example, 80% ormore of the upper region thereof.

Referring to FIG. 18A and FIG. 18B, a first pad electrode 331 and asecond pad electrode 332 are formed on the first contact electrode 341and the second contact electrode 342, respectively. The first padelectrode 331 and the second pad electrode 332 may be formed of the samemetal by the same process. For example, the first and second padelectrodes 331, 332 may be composed of a Ti layer (300 Å)/Au layer(7,000 Å)/Ti layer (50 Å).

Before formation of the first and second pad electrodes 331, 332, ananti-step layer (see FIG. 2 and FIG. 3) may be additionally formed onthe first contact electrode 341.

Referring to FIG. 19A and FIG. 19B, a passivation layer 360 havingopenings 360 a, 360 b formed to expose the surfaces of the first andsecond pad electrodes 331, 332 is formed. The opening 360 a exposes thefirst pad electrode 331 around the mesa M and the opening 360 b exposesthe second pad electrode 332 on the mesa M.

The passivation layer 360 may be formed by forming an insulation layerover the entire upper surface of the substrate 310, followed by etchingto expose the first and second pad electrodes 331, 332.

Then, a first bump electrode 351 and a second bump electrode 352 areformed on the first and second pad electrodes 331, 332, respectively,and an anti-reflection layer 370 is formed on the lower surface of thesubstrate 310, followed by dividing into individual light emittingdevices, thereby completing the light emitting device 300, as shown inFIG. 14. The anti-reflection layer 370 may be omitted.

The first and second bump electrodes 351, 352 cover the openings 360 a,360 b to contact the surfaces of the pad electrodes 331, 332, and may beformed to cover some regions on the surface of the passivation layer160. In addition, as shown in FIG. 14, the first bump electrode 351 ispartially placed in an upper region of the mesa M. With this structure,a portion of the first bump electrode 351 may be flush with the secondbump electrode 352 in the upper region of the mesa M.

On the other hand, as in the exemplary embodiment described above,anti-step patterns may be formed in the openings 360 a, 360 b, or may beomitted.

FIG. 20 to FIG. 23 are plan views of light emitting devices 300 a, 400,500, and 600 according to exemplary embodiments of the presentinvention.

Referring to FIG. 20, a light emitting device 300 a according to anexemplary embodiment is generally similar to the light emitting device300 described above except for the location and shape of the second bumpelectrode 352. Specifically, in the light emitting device 300 describedabove, the second bump electrode 352 is placed within the upper regionof the mesa M, whereas the second bump electrode 352 according to theillustrated exemplary embodiment is formed in a substantiallyrectangular shape and partially covers upper regions of the indentationsbetween the sub-branches. That is, the second bump electrode 352overlaps the first contact electrode 341 and the first pad electrode331, instead of being disposed within the upper region of the mesa M. Inthis exemplary embodiment, the second bump electrode 352 is insulatedfrom the first pad electrode 331 and the first contact electrode 341 bythe passivation layer 360.

According to this exemplary embodiment, since the second bump electrode352 is placed outside the region of the mesa M, the size of the secondbump electrode 352 can be further increased, thereby improving bondingstrength upon bonding to a submount and the like.

Referring to FIG. 21, a light emitting device 400 according to thisexemplary embodiment includes a substrate 410, a light emitting stack(e.g., light emitting diode), which includes a first conductivity-typesemiconductor layer 421, an active layer, and a second conductivity-typesemiconductor layer, a first contact electrode 441, a second contactelectrode 442, a first pad electrode 431, a second pad electrode 432, apassivation layer 460, a first bump electrode 451, and a second bumpelectrode 452. The light emitting device 400 may further include ananti-reflection layer.

The light emitting device 400 according to this exemplary embodiment isgenerally similar to the light emitting device 300 except for the shapeof the mesa M and the locations and shapes of the first bump electrode451 and the second bump electrode 452. Repeated description of the samecomponents will be omitted in order to avoid redundancy.

A mesa M of the light emitting device 400 includes a main branch Mb andsub-branches Sb, and has indentations Cp placed between the sub-branchesSb. The main branch Mb is disposed along the edge of the substrate 410,and each of the sub-branches Sb extends at a predetermined angle fromthe main branch Mb. The main branch Mb may be continuously formed alongtwo adjacent edges of the substrate 410 having a rectangular shape andthe sub-branches Sb may extend from the main branch Mb to be parallel toeach other.

Alternatively, the main branch Mb may be restrictively disposed near oneedge of the substrate 410, and the sub-branches Sb may extend from themain branch Mb.

The sub-branches Sb may have different lengths and may be disposedparallel to a diagonal line of the substrate 410.

The first bump electrode 451 is electrically connected to the first padelectrode 431 through an opening 460 a of the passivation layer 460, andthe second bump electrode 452 is electrically connected to the secondpad electrode 432 through an opening 460 b of the passivation layer 460.The first bump electrode 451 covers the opening 460 a to seal theopening 460 a and partially covers the passivation layer 460. The secondbump electrode 452 also covers the opening 460 b to seal the opening 460a and partially covers the passivation layer 460.

The first bump electrode 451 and the second bump electrode 452 haverectangular shapes and are disposed to face each other. Accordingly,both of the first bump electrode 451 and the second bump electrode 452partially overlap the mesa M and also partially overlap the indentationsCp of the mesa M.

Referring to FIG. 22, a light emitting device 500 according to thisexemplary embodiment includes a substrate 510, a light emitting stack(e.g., light emitting diode), which includes a first conductivity-typesemiconductor layer 521, an active layer, and a second conductivity-typesemiconductor layer, a first contact electrode 541, a second contactelectrode 542, a first pad electrode 531, a second pad electrode 532, apassivation layer 560, a first bump electrode 551, and a second bumpelectrode 552. The light emitting device 500 may further include ananti-reflection layer.

The light emitting device 500 according to this exemplary embodiment isgenerally similar to the light emitting device 300 except for the shapeof the mesa M, the locations and shapes of the first bump electrode 551and the second bump electrode 552, and the locations and shapes ofopenings 560 a, 560 b of the passivation layer 560. Repeated descriptionof the same components will be omitted in order to avoid redundancy.

The mesa M of the light emitting device 500 occupies a larger area ofthe substrate 510 than the mesa M of the light emitting device 300. Forexample, the width and length of the main branch Mb and the sub-branchesSb may be greater than the width and length of the main branch and thesub-branches of the light emitting device 300.

The openings 560 a may be disposed outside the indentations of the mesaM and outside the mesa M to be separated from each other. In addition,the openings 560 b may be disposed on the sub-branches Sb of the mesa Mto be separated from each other. Two or more openings 560 b may bedisposed on each sub-branch Sb.

The first bump electrode 551 is electrically connected to the first padelectrode 531 through the openings 560 a of the passivation layer 560,and the second bump electrode 552 is electrically connected to thesecond pad electrode 532 through the openings 560 b of the passivationlayer 560. The first bump electrode 551 covers the openings 560 a toseal the openings 560 a and partially covers the passivation layer 560.The second bump electrode 552 also covers the openings 560 b to seal theopenings 560 a and partially covers the passivation layer 560.

The first bump electrode 551 and the second bump electrode 552 haverectangular shapes and are disposed to face each other. Accordingly,both of the first bump electrode 551 and the second bump electrode 552partially overlap the mesa M and also partially overlap the indentationsCp of the mesa M.

Referring to FIG. 23, a light emitting device 600 according to thisexemplary embodiment includes a substrate 610, a light emitting stack(e.g., light emitting diode), which includes a first conductivity-typesemiconductor layer 621, an active layer, and a second conductivity-typesemiconductor layer, a first contact electrode 641, a second contactelectrode 642, a first pad electrode 631, a second pad electrode 632, apassivation layer 660, a first bump electrode 651, and a second bumpelectrode 652. The light emitting device 600 may further include ananti-reflection layer.

The light emitting device 600 according to this exemplary embodiment isgenerally similar to the light emitting device 300 except for the shapeof the mesa M, the locations and shapes of the first bump electrode 651and the second bump electrode 652, and the locations and shapes ofopenings 660 a, 660 b of the passivation layer 660. Repeated descriptionof the same components will be omitted in order to avoid redundancy.

The mesa M of the light emitting device 600 occupies a larger area ofthe substrate 610 than the mesa M of the light emitting device 300, andis divided into a plurality of regions. The mesa includes an indentationCp placed in each of the divided regions.

The openings 660 a may be disposed between the divided regions of themesa M and outside the mesa M to be separated from each other. Inaddition, the openings 660 b may be disposed in each of the dividedregions on the mesa M to be separated from each other.

The first bump electrode 651 is electrically connected to the first padelectrode 631 through the openings 660 a of the passivation layer 660,and the second bump electrode 652 is electrically connected to thesecond pad electrode 632 through the openings 660 b of the passivationlayer 660. The first bump electrode 651 covers the openings 660 a toseal the openings 660 a and partially covers the passivation layer 660.The second bump electrode 652 also covers the openings 660 b to seal theopenings 660 a and partially covers the passivation layer 660.

The first bump electrode 651 and the second bump electrode 652 haverectangular shapes and are disposed to face each other. Accordingly,both of the first bump electrode 651 and the second bump electrode 652partially overlap the mesa M and also partially overlap the indentationsCp of the mesa M.

Each of the light emitting devices 300 a, 400, 500, and 600 describedabove can be fabricated into a light emitting device package asdescribed with reference to FIG. 13.

Although some exemplary embodiments have been described herein, itshould be understood that these embodiments are given by way ofillustration only, and that various modifications, variations, andalterations can be made by those skilled in the art without departingfrom the spirit and scope of the present invention.

That is, it should be understood that these embodiments are provided forillustration only and are not to be construed in any way as limiting thepresent invention. For example, each of components described as a singlecomponent may be embodied as dispersed components, and componentsdescribed as dispersed components may also be embodied as a coupledcomponent.

In addition, a component described in a specific exemplary embodimentmay also be applied to other exemplary embodiments without departingfrom the scope of the present invention.

Therefore, it should be understood that the scope of the presentinvention is limited only by the appended claims and all modifications,variations, and alterations deducible from the appended claims andequivalents thereto fall within the scope of the present invention.

1. A UV light emitting device comprising: a substrate; a firstconductivity-type semiconductor layer disposed on the substrate; a mesadisposed on the first conductivity-type semiconductor layer, andcomprising a second conductivity-type semiconductor layer and an activelayer interposed between the first conductivity-type semiconductor layerand the second conductivity-type semiconductor layer; a first contactelectrode contacting the first conductivity-type semiconductor layerexposed around the mesa; a second contact electrode disposed on the mesaand contacting the second conductivity-type semiconductor layer; apassivation layer covering the first contact electrode, the mesa, andthe second contact electrode, and comprising openings disposed on thefirst contact electrode and the second contact electrode; and a firstbump electrode and a second bump electrode electrically connected to thefirst contact electrode and the second contact electrode through theopenings of the passivation layer, respectively, wherein the mesa has aplurality of indentations in plan view and each of the first bumpelectrode and the second bump electrode covers the openings of thepassivation layer and a portion of the passivation layer.
 2. The UVlight emitting device of claim 1, wherein the first contact electrodecontacts the first conductivity-type semiconductor layer at least in theindentations of the mesa.
 3. The UV light emitting device of claim 1,further comprising: a first pad electrode disposed on the first contactelectrode; and a second pad electrode disposed on the second contactelectrode, wherein the openings of the passivation layer expose thefirst pad electrode and the second pad electrode, and the first bumpelectrode and the second bump electrode are connected to the first padelectrode and the second pad electrode through the openings,respectively.
 4. The UV light emitting device of claim 3, wherein thefirst pad electrode and the second pad electrode comprise the samemetallic material.
 5. The UV light emitting device of claim 4, furthercomprising: a step pad layer interposed between the first contactelectrode and the first pad electrode.
 6. The UV light emitting deviceof claim 3, further comprising: an anti-step pattern disposed on thefirst pad electrode and the second pad electrode.
 7. The UV lightemitting device of claim 1, wherein: the openings of the passivationlayer exposing the first contact electrode are separated from the mesa;and the openings of the passivation layer exposing the second contactelectrode are disposed within an upper region of the mesa.
 8. The UVlight emitting device of claim 1, wherein the first contact electrodesurrounds the mesa.
 9. The UV light emitting device of claim 1, whereinthe indentations have an elongated shape in the same direction.
 10. TheUV light emitting device of claim 1, wherein the substrate comprises atleast one of a silicon (Si) substrate, a zinc oxide (ZnO) substrate, agallium nitride (GaN) substrate, a silicon carbide (SiC) substrate, analuminum nitride (AlN) substrate, and a sapphire substrate.
 11. The UVlight emitting device of claim 1, wherein the mesa has a mirror symmetrystructure.
 12. The UV light emitting device of claim 1, wherein the mesahas a main branch and a plurality of sub-branches extending from themain branch.
 13. The UV light emitting device of claim 1, wherein aportion of the first bump electrode is disposed on the mesa to overlapthe mesa, the first bump electrode being spaced apart from the mesa bythe passivation layer.
 14. The UV light emitting device of claim 1,wherein the openings of the passivation layer disposed on the firstcontact electrode are partially placed in the indentations.
 15. The UVlight emitting device of claim 1, wherein the first bump electrode issymmetrically disposed at opposite sides of the second bump electrodesuch that the second bump electrode is interposed therebetween.
 16. TheUV light emitting device of claim 15, wherein the first bump electrodeis integrally connected.
 17. The UV light emitting device of claim 1,wherein the second bump electrode has an arc-shaped end portion.
 18. TheUV light emitting device of claim 17, wherein the second bump electrodecomprises a plurality of unit electrodes connected to each other by aconnecting portion.
 19. The UV light emitting device of claim 1, wherein the UV emitting device is configured to emit deep UV light having awavelength of 360 nm or less.
 20. A UV light emitting device comprising:a substrate; a first conductivity-type semiconductor layer disposed onthe substrate; a mesa disposed on the first conductivity-typesemiconductor layer, and comprising a second conductivity-typesemiconductor layer and an active layer interposed between the firstconductivity-type semiconductor layer and the second conductivity-typesemiconductor layer; a first contact electrode contacting the firstconductivity-type semiconductor layer exposed around the mesa; a secondcontact electrode disposed on the mesa and contacting the secondconductivity-type semiconductor layer; a passivation layer covering thefirst contact electrode, the mesa, and the second contact electrode, andcomprising openings disposed on the first contact electrode and thesecond contact electrode; and a first bump electrode and a second bumpelectrode electrically connected to the first contact electrode and thesecond contact electrode through the openings of the passivation layer,respectively, wherein the mesa has a plurality of indentations in planview and some of the openings of the passivation layer are disposedoutside the mesa and the indentations.
 21. The UV light emitting deviceof claim 20, wherein the passivation layer further comprises openingsdisposed inside the indentations, and the openings disposed inside theindentations are connected to each other through the openings disposedoutside the indentations.
 22. The UV light emitting device of claim 20,wherein the passivation layer further comprises openings disposed insidethe indentations, and the openings disposed inside the indentations areseparated from each other.